This invention relates to assay cartridges suitable for use in automated analytical systems employing a conveyor for transport of such cartridges among various work stations and, more particularly, to a cartridge which is provided with a spring catch for securing the cartridge in a nest on the conveyor.
Various types of chemical tests can be performed by automated test equipment, an example of testing of considerable interest being the assay of biological substances for human health care. Automated test equipment allows large numbers of test samples to be processed rapidly. Such equipment is employed in health care institutions including hospitals and laboratories. Biological fluids, such as whole blood, plasma or serum are tested to find evidence of disease, to monitor therapeutic drug levels, etc.
In the automated test instrument a sample of the test fluid is typically provided in a sample cup and all of the process steps including pipetting of the sample onto an assay test element, incubation and readout of the signal obtained are carried out automatically. The test instrument typically includes a series of work stations each of which performs a specific step in the test procedure. The assay element or cartridge is typically transported from one work station to the next by means of a conveyor such as a carousel to enable the test steps to be accomplished sequentially. The conveyor usually carries a plurality of the assay cartridges, each secured to a specific location on the upper surface of the conveyor. In the usual arrangement, the assay cartridges are spaced apart from each other in berths which are located along the periphery of the conveyor to facilitate automatic insertion and extraction.
It is necessary to construct the berths for the assay cartridges in a fashion which permits the cartridge to be inserted readily without any binding along the walls of the berth. Such binding or any other such impediment would interfere with precise placement of the cartridge within its berth. Similarly, upon extraction of the cartridge, there should be no binding or other impediment which might interfere with the operation of the automated analytical instrument. Consequently, it has been the practice to construct the berths with smooth interior surfaces which allow the cartridges to be slid readily into and out of the berths.
Another important consideration is the need to ensure that the assay cartridges are precisely positioned on the conveyor and further, that they are not displaced from their positions during movement of the conveyor. The precise positioning of the assay cartridges is necessary for proper operation of the instrument. For example, the fluid dispensing assembly typically includes a pipette which obtains sample fluid from a sample cup and is then transported to the assay cartridge to dispense the required volume of sample fluid. Any excessive misalignment of the pipette with assay cartridge could result in spillage or an incorrect volume being deposited on the assay element thereby causing inaccurate test results.
As a result of the aforementioned smooth-walled berths and correspondingly smooth-walled assay cartridges, the latter may not be held as securely in their respective positions as would be desirable. Accordingly, it is an object of this invention to provide an assay cartridge which can be securely held in its required location on a conveyor while at the same time being readily inserted into and removed from such location.